1. Field of the Invention
The present invention relates to an ink-on-demand ink jet recording apparatus, and to a manufacturing method for an ink jet head therefor.
2. Description of the Related Art
Ink jet printers offer numerous desirable features, including extremely quiet operation when printing, especially at high speed, a high degree of freedom in the choice of ink, and the ability to use low-cost plain paper. So-called "ink-on-demand" printer heads in which ink is ejected only when required during recording have become the mainstream because it is not necessary to recover ink ejected unnecessarily during recording.
The ink jet head disclosed in JP-B-8316/1987 is one type of ink-on-demand ink jet head according to the prior art. In this type of head, a filter disposed in the ink supply path of the ink jet head is formed simultaneously with the ink passage by a photo-etching process, resulting in an ink jet head comprising an internal filter enabling ink to be ejected stably. The filter prevents foreign particulate from partially or fully blocking the flow of ink in the ink jet head and various passages therein.
The cross-sectional area of the filter opening preventing penetration of foreign particulate into the ink jet head must be smaller than the cross-sectional area of the any other ink passages consisting of nozzles, ejection chambers, ink supply cavity, and orifices communicating with the ejection chambers and ink supply cavity. In the above-described ink jet head, however, the filter is formed simultaneously with the other ink passages by an isotropic etching method, and the depth of the filter is therefore substantially the same as the depth of the nozzles and the orifices. As a result, the size of foreign particulate passing through the filter may be the same size as the nozzle and orifices. The probability of a nozzle or orifices becoming clogged is therefore high, and it is not possible to completely prevent clogging of all nozzles and orifices. This characteristic has a tendency to reduce the print quality and ink jet head reliability.
Further, the following problems are presented by simply forming the filter inside the head as in the above ink jet head, and achieving such a head is difficult.
The ink supply cavity distributes or supplies the ink to the ejection chamber through the orifices, and simultaneously buffers or reduces the pressure caused by the back flow of ink from the ink ejection chambers when the ink is ejected from the nozzle.
When the inertance of the filter is high, the pressure caused by ink back flow from the ink ejection chambers when ink is ejected from the nozzle cannot be sufficiently absorbed or reduced. This characteristic has a tendency to cause a pressure increase in the ink supply cavity, introducing pressure interference between the other ink ejection chambers and causing ink to be ejected from the other nozzles for which the pressure generating means has not been operated (i.e., ink is ejected from non-driven nozzles). If the flow resistance of the filter channel is high, ink cannot be sufficiently supplied from the filter to the ink supply cavity. The ejected ink volume therefore drops, air is taken in from the nozzle, and consistent ink ejection cannot be assured. Additionally, when the ink volume of the ink supply cavity is low, pressure cannot be sufficiently absorbed or reduced. Pressure interference between the ink ejection chambers therefore occurs, as when the filter inertance is high, and ink is ejected from nozzles of which the pressure generating means has not been operated.
In each of these cases, print reliability drops because of missing, incompletely formed or extra pixels in the printed image, contributing to indefinite images, reading errors and reduced print quality.
When the filter is formed using glass or another isotropic material, the etching ratio is not stable, and it is difficult to manufacture an ink jet head in which the filter is formed easily and with good precision.